#!/bin/bash

function valid() {
    regex="^(1\s){0,1}\([0-9]{3}\) [0-9]{3} [0-9]{4}$"
    if [[ "$1" =~ $regex ]]; then
        echo "valid"
    else
        echo "invalid"
    fi
}

valid "(765) 123 4567"
valid "1 (765) 123 4567"
valid "1(765) 123 4567"
valid "123 456 78910"
valid "123 4567"