I want to check that any phone number entered MUST start with a Zero

I’m working with a materialui component and I’m trying to get the input to force the user to start with a 0 when entering a phone number. We have a dropdown on the side that specifies that Areacode and I want to keep things nice and clean.

My issue is that I’m not that clued up on regular expressions and if that is even the way to go about solving this issue?

Can someone please help me out with suggestions?