Phone trackers record every drive and then ask you to sort them. This works the other way round: you add only the trips that count, and the total is the deduction you can show.
Most self-employed people lose money by guessing at year end. A weekly five-minute entry session catches the trips you would forget. If you drive the same route on set days, use the repeat feature to fill a whole quarter at once and then edit the exceptions.
What to keep
Keep the PDF with your return papers, and keep the spreadsheet if your accountant likes one. The IRS can ask for records for several years after you file.
Distances come from OpenStreetMap routing when you press the lookup button, or you can type the odometer figure. A figure you measured yourself is stronger evidence than a map estimate.