Require proper phone entry

I’m trying to figure out a way to require a user to enter ALL 10 digits in the phone field. A mask does no good. They can still enter just a few digits. What’s happening is that users sometimes just enter a few digits. Not the whole phone number. I would like to make it (while using Rules, I suppose) that ANYTHING less than a full phone number will hide the Submit button. I found some regex scripts that say they will do this. I’m not familiar with regex and couldn’t get them to work.

Please help

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