Can my girlfriend drop the charges if I broke her phone, had me arrested and pressed charges but I bought her a new phone a week after incident?

Your girlfriend can ask the DA to drop the case. She is considered a complaining witness, but still just a witness to a crime committed against the laws of the state. They will take her into consideration and if she tells that that full restitution was made for the property it is a possibility that the State would drop the charges. This is assuming that you were charged with criminal mischief and not interference with an emergency phone call. You should consult with your criminal defense attorney about the matter.