what is the penalty for going through my wifes phone

If your wife gave you her password to her phone  it is permission to go into it.  If she did not give you permission then you are a hacker and will have created liability for yourself.   As to your wife's cheating, you should think about speaking with a divorce and separation lawyer.   You may want to discuss your situation with a lawyer in more detail. Many lawyers  offer a free phone consultation.