Need Phone Validation for Domestic & International

So I've searched and tried various validations in different posts from here to stackexchange to reddit.

I am looking for a validation where in the Phone field, the number can be either domestic or international but must start with a + symbol.  

US numbers need to have the 1 country code, so should look like +1xxxxxxxxxx.

International numbers need to start with a + and then the country code so like +44xxxxxxxxxx.

Always with a + and NO dashes in btwn.

Has anyone successfully done this please?  TIA!!!