Safety glass

You don't need anything. Screen protectors have their own special glue (so that, if needed, you can easily detach them).

Generally they are used along with a silicon TPU back cover (transparent or colored)

Whether or not to add a screen protector is a personal decision. I’ve never had one on an iPhone, but I take good care of my phone, always putting it in a slipcase or holster when not using it. Ive never dropped any cell phone (well, hardly ever), going back 30 years of using them. However, if you carry a phone loose in a pocket with keys and coins then either a wrap-around case or a screen protector is a good idea. Note that a screen protector will not protect against breakage if you drop your phone; its primary function is to protect against scratches.

I did use screen protectors on my Palm Treo, which had a plastic screen rather than glass, and which would scratch easily, but not on iPhones.

I too am VERY careful w/ my phone, keeping it holstered when not in use; but I often work in harsh, wet, exposed, dusty, and generally “disagreeable” industrial construction environments.

I DO use a glass screen protector on my Xs Max. (along w/ a heavy, “ruggedized” rubber case)

Dunno if it’s helped, but it certainly hasn’t hurt. (It’s taken more than a few falls when the entire holster has come off my belt)

When uncased for cleaning, my 33-month old, heavily-used, and well-travelled iPhone looks brand new.

FWIW, here’s a short video showing Otterbox’s screen protector install process:

https://youtu.be/7di7PGrEQ4w

One downside to a screen protector is it defeats the “oliophobic” coating on the screen that prevents fingerprints from clouding the screen.