Grabbing her by the wrists and pushing her IS assault, so is grabbing her phone as I assume you forcefully snatched it off her?
Her statement is evidence and there may be evidence of aggression , texts for example, on your phone. You are NOT being prosecuted unjustly. You need to think again about pleading not guilty. If you go to court and plead not guilty you are going to lose the case.
You need to apologise and plead guilty, if you do this there is a good chance the case will be dropped or you will get a conditional discharge.