The leaflet text provided for this section gives no information about maprotiline taken together with phenytoin. It covers electroshock therapy, thyroid medicines and guanethidine, and then stops in the middle of a sentence ("The risk of"), so any phenytoin interaction that may follow is cut off. Because I can't state an effect that the text doesn't give, I can't write a reliable explanation for this pair from this passage. If you can send the full sentence that mentions phenytoin, I will rewrite it right away.
These medicines can affect each other in a serious way. Do not start taking them together unless your doctor has said it is OK. If you already take both, do not stop either one on your own: speak to your doctor or pharmacist soon.