I don't use GV as it's not free where I live, so it's good that you feed me this info
x. means none or more digits. Only digits, so it would not include "+". Trying again:
@.88351x.
This means none or more alphanumeric characters, followed by 88351, followed by none or more digits. It should cover all the cases you mentioned.
It may seem like a lot of trouble, but that xx. rule can create a lot of problems! Of course, if you do not use iNum, then there's no need to replace the xx. rule with anything.