Placeholder plugin for Gravity Forms http://www.wpbeginner.com/plugins/gravity-forms-most-beginner-friendly-wordpress-contact-form-plugin/

gform-placeholder.php

<?php
/* Add a custom field to the field editor (See editor screenshot) */
add_action("gform_field_standard_settings", "my_standard_settings", 10, 2);

function my_standard_settings($position, $form_id){

// Create settings on position 25 (right after Field Label)

if($position == 25){
?>
		
<li class="admin_label_setting field_setting" style="display: list-item; ">
<label for="field_placeholder">Placeholder Text

<!-- Tooltip to help users understand what this field does -->
<a href="javascript:void(0);" class="tooltip tooltip_form_field_placeholder" tooltip="&lt;h6&gt;Placeholder&lt;/h6&gt;Enter the placeholder/default text for this field.">(?)</a>
			
</label>
		
<input type="text" id="field_placeholder" class="fieldwidth-3" size="35" onkeyup="SetFieldProperty('placeholder', this.value);">
		
</li>
<?php
}
}

/* Now we execute some javascript technicalitites for the field to load correctly */

add_action("gform_editor_js", "my_gform_editor_js");

function my_gform_editor_js(){
?>
<script>
//binding to the load field settings event to initialize the checkbox
jQuery(document).bind("gform_load_field_settings", function(event, field, form){
jQuery("#field_placeholder").val(field["placeholder"]);
});
</script>

<?php
}

/* We use jQuery to read the placeholder value and inject it to its field */

add_action('gform_enqueue_scripts',"my_gform_enqueue_scripts", 10, 2);

function my_gform_enqueue_scripts($form, $is_ajax=false){
?>
<script>

jQuery(function(){
<?php

/* Go through each one of the form fields */

foreach($form['fields'] as $i=>$field){

/* Check if the field has an assigned placeholder */
			
if(isset($field['placeholder']) && !empty($field['placeholder'])){
				
/* If a placeholder text exists, inject it as a new property to the field using jQuery */
				
?>
				
jQuery('#input_<?php echo $form['id']?>_<?php echo $field['id']?>').attr('placeholder','<?php echo $field['placeholder']?>');
				
<?php
}
}
?>
});
</script>
<?php
}
?>