This code adds custom filters to the member directory of the Ultimate Member plugin. These filters are grouped - one filter searches in multiple fields.

um_grouped_filters.php

<?php

/**
 * Add custom grouped filters to the member directory.
 *
 * Add filters you need to this array. Every filter is an array where:
 *  - key    Filter key. Any valid string key.
 *  - type   Filter type. Accepts: 'text', 'select'.
 *  - label  Filter label (used as the filter placeholder).
 *  - fields An array of usermeta keys. Filter searches a value in these usermeta.
 */
$um_custom_filters = array(
	array(
		'key'    => 'my_phone',
		'type'   => 'text',
		'label'  => 'Phone',
		'fields' => array(
			'mobile_number',
			'phone_number',
		),
	),
	array(
		'key'    => 'my_hobby',
		'type'   => 'select',
		'label'  => 'Hobby',
		'fields' => array(
			'um_pet',
			'um_sport',
		),
	),
);

global $um_custom_filters;

// Add custom filters.
add_filter( 'um_frontend_member_search_filters', function( $search_filters ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		$search_filters[] = $f['key'];
	}
	return $search_filters;
} );

// Add custom filter labels.
add_filter( 'um_members_directory_filter_fields', function( $filter_fields ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		$filter_fields[ $f['key'] ] = $f['label'];
	}
	return $filter_fields;
} );

// Add custom filter types.
add_filter( 'um_members_directory_filter_types', function( $filter_types ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		$filter_types[ $f['key'] ] = $f['type'];
	}
	return $filter_types;
} );

// Add custom filter options.
add_filter( 'um_search_fields', function( $attrs, $field_key ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as &$f ) {
		if ( $field_key === $f['key'] ) {
			$attrs = array_merge( $attrs, $f );

			if ( 'select' === $f['type'] ) {
				$attrs['type']    = 'select';
				$attrs['metakey'] = current( $f['fields'] );

				// prepare dropdown options.
				$f['options'] = array();
				foreach ( $f['fields'] as $field_key ) {
					$field_data = UM()->fields()->get_field( $field_key );
					if ( $field_data && ! empty( $field_data['options'] ) ) {
						$f['options'] = array_merge( $f['options'], $field_data['options'] );
					}
				}
				sort( $f['options'] );
				$attrs['options'] = $f['options'];
			}
		}
	}
	return $attrs;
}, 10, 2 );

// Combine options for the filter type "select".
add_filter( 'um_member_directory_filter_select_options_sorted', function( $options, $attrs ) {
	global $um_custom_filters;
	if ( isset( $attrs['key'] ) ) {
		foreach( $um_custom_filters as $f ) {
			if ( $attrs['key'] === $f['key'] && ! empty( $f['options'] ) ) {
				$options = (array) $f['options'];
			}
		}
	}
	return $options;
}, 10, 2 );

// Modify the um_get_members query (default usermeta table).
add_filter( 'um_prepare_user_query_args', function( $query_args, $directory_data ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		if ( ! empty( $_POST[ $f['key'] ] ) && ! empty( $f['fields'] ) ) {
			$filter_query = array(
				'relation' => 'OR',
			);

			switch ( $f['type'] ) {
				default:
				case 'text':
					$value = sanitize_text_field( $_POST[ $f['key'] ] );
					foreach ( $f['fields'] as $field ) {
						$filter_query[] = array(
							'key'     => $field,
							'value'   => $value,
							'compare' => 'LIKE',
						);
					}
					break;

				case 'select':
					$values_input = map_deep( $_POST[ $f['key'] ], 'sanitize_text_field' );
					foreach ( $values_input as $value ) {
						foreach ( $f['fields'] as $field ) {
							$filter_query[] = array(
								'key'     => $field,
								'value'   => serialize( trim( $value ) ),
								'compare' => 'LIKE',
							);
						}
					}
					break;
			}

			$query_args['meta_query'][] = $filter_query;
		}
	}
	return $query_args;
}, 99, 2 );

// Modify the um_get_members query (custom usermeta table).
add_action( 'um_pre_users_query', function( $directory, $directory_data ) {
	global $wpdb;
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		if ( ! empty( $_POST[ $f['key'] ] ) && ! empty( $f['fields'] ) ) {

			$table = $wpdb->prefix . 'um_metadata';
			$alias = 'umm' . $f['key'];
			$keys  = "'" . implode( "','", $f['fields'] ) . "'";

			switch ( $f['type'] ) {
				default:
				case 'text':
					$value = sanitize_text_field( $_POST[ $f['key'] ] );
					$like  = '%' . $wpdb->esc_like( $value ) . '%';

					$filter_query = $wpdb->prepare(
						"INNER JOIN %i AS %i ON ( %i.user_id = u.ID AND %i.um_key IN ({$keys}) AND %i.um_value LIKE %s )",
						$table,
						$alias,
						$alias,
						$alias,
						$alias,
						$like
					);
					break;

				case 'select':
					$values_input = map_deep( $_POST[ $f['key'] ], 'sanitize_text_field' );
					$values_array = array();
					foreach ( $values_input as $value ) {
						$like  = '%' . $wpdb->esc_like( serialize( trim( $value ) ) ) . '%';

						$values_array[] = $wpdb->prepare(
								"%i.um_value LIKE %s",
								$alias,
								$like
						);
					}
					$values = implode( ' OR ', $values_array );

					$filter_query = $wpdb->prepare(
						"INNER JOIN %i AS %i ON ( %i.user_id = u.ID AND %i.um_key IN ({$keys}) AND ({$values}) )",
						$table,
						$alias,
						$alias,
						$alias,
						$alias
					);
					break;
			}

			$directory->joins[] = $filter_query;
		}
	}
}, 10, 2 );

This code snippet is a part of the article Use a single control to filter by several fields in the members directory