As an ex-sheriff, why don't you just tell everyone that they are looking for cell phone use?
These people all think they're above the law to use their phones so tell them you're going to be out in force and they won't use them till the next day. Increase the fines for use to to a large amount.
I have seen police sitting right next to people using their phones and they don't even look twice. It's sad that people think they are above the law and do it anyway.