This is code for checking the validity of phone numbers for Event Manager

check_phone_number.rb

def check_valid_phone_number(phone_number)
  number_length = phone_number.length

  if number_length == 10
    phone_number
  elsif number_length == 11 and phone_number[0] == '1'
    phone_number[1..10]
  else
    invalid_number
  end
end

def invalid_number
  'Invalid number'
end

This is great because it reduces the the use of the 'Invalid number' string in multiple places.

Second, you could combine the nested if statements for the length 11 numbers that start with a '1'

Third, when the number is less than 10 and greater than 10 it is valid number so you might want to just rely on your number_length explicit checks of 10 and 11.