<soapbox> I agree about the "pet peeve". Often, I try to register on a US site and it won't accept my UK phone number.
Even UK systems screw up since we often have number changes and the websites often don't change quickly enough.
Suggestion (adding to comments by [id://kjherron]) :

Allow any format, strip down to digits, and check for a reasonable number of digits to allow for international dialing codes, etc. then leave it at that.

If you want real validation, you'll need to check the dialing codes for each potential country to see if they are OK, and KEEP THE DATABASE UP-TO-DATE.
</soapbox>
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Brovnik

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