Well it depends, for instance if you want to test with an OR operator, this would be something like this :
var mergedRegex = /^(([7-9])[0-9]{9}|(0)[7-9][0-9]{9}|(\+91)[7-9][0-9]{9})$/;
If you want with an AND operator, try this instead :
var mergedRegex = /^(?=([7-9])[0-9]{9})(?=(0)[7-9][0-9]{9})(?=\+91)[7-9][0-9]{9})$/;
solved how to combine regex in jquery?