Check the length of value isnumeric jquery

Telephone:

if (!$.isNumeric($("#phone").val())) {

alert("error invalid number");

    }

I am making a simple form that allows the user to sign up but my problem is how to avoid the user should not click only 1 length of value. let I say the length should less than 7, I'll try to add && $("#phone").val().length < 7 in if statement. but it wont work :(