I have a similar situation.
People enter a phone number.
They enter things
like +31 6 123 45 678
or +31612345678
or 316 1234 5678
or 06-1234 5678
ect., etc..
I want them always to be stored like: +31612345678
Where to I place my substitude formula, because if I place it in the ‘Initial Value’, than that won’t work.
You can do that for example with an action. You can trigger it from the form view’s option called Event action. It means it triggers that action every time you save the form.