Truecaller app - how get back to speaker phone?

Sorry to plunk this down on the Android forum but I can't find any other place. I have the new Google phone. Soooooo love it! I switched over from Mr. Number to TrueCaller. I like it however there is one thing I can't figure out. On a call, if I select speaker phone, and then decide to change back from speakerphone to handset, I can't figure out how to get back to a screen that will allow me to do so. Does anyone know how to change from speakerphone back to handset? -Thank you