Question

I want a regular expression to match a string that may or may not start with plus symbol and then contain any number of digits.

Those should be matched

[phone]
or
3423564564

Answer 1

This should work

\+?\d+

Matches an optional + at the beginning of the line and digits after it

EDIT:

As of OP’s request of clarification: 3423kk55 is matched because so it is the first part (3423). To match a whole string only use this instead:

^\+?\d+$