We are trying to use the regex feature to prevent customers from entering the wrong format for their phone number. It does work in limited circumstances, however it is very challenging to write a complete regex because of the fact that the phone number formatter at checkout is buggy. Seemingly randomly, it will format the phone numbers in different groupings for the same length of string. E.g., a 9 digit phone number will be formatted as 3-3-3 and another will be formatted as 3-4-2, another as 4-3-1 and so on. This is not limited to 9 digit phone numbers, the same is true for 10 and 11 digit phone numbers. Some will be formatted as 3-4-4, others as 3-3-5. Writing a concise regex is therefore very complicated and will not work for its intended use case.
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