I need to add a validation error message for an input in Flow.

I have a Phone field where I have maintaned a validation, where the phone number should be of length 10, it should not start with 1. I'm using the below formula.
 AND( LEN({!School_Phone_Key})=10,
NOT(REGEX({!School_Phone_Key} ,"^[a-z A-Z]*$")) ,
NOT(LEFT({!School_Phone_Key}, 1) = "1")
)

Now I also need to check if any symbol is presnt in the field, it should be restricted if the 10 digit number has any symbol. Can someone please guide me with the formula.