I'm afraid that's not enough.
Down inside there is a tiny flash memory chip around 10x15mm in size. Easy for the M police to desolder that and put it into a usb ziff socket or solder it to another phone and see all your mucky top down browsing history.
Chucking the phone in your pint, Factory reset, delete or format won't clear your filthy Miata/MX5 photos off of that chip.
You gotta find that chip and put a drill through it. Or shred the whole phone.
Or chuck it into that bottom drawer with all the other old phones and chargers.