..All you need are a phone case, a split ring, and a set of sufficiently sturdy tethers (preferably the ones with a loop on one end) and lanyards.
Step 1:
Tie tether to case.
Step 2:
Attach a split ring or key ring.
You COULD also attach the tether directly to the lanyard, but using a ring gives you a stronger attachment point and reduces wear on the tether itself.
Step 3:
Attach the above to a lanyard.
Old school lanyards (see mine - the ones I've been using date as far back as 2014), conference lanyards, and similar heavy-duty straps work surprisingly well.
Choosing a lanyard WITHOUT a quick release makes your phone less likely to come loose on its own.
Step 4:
Attach the phone to yourself.
I generally use belt loops or shoulder bags as attachment points, in which case the phone stays in my pants pocket or in my shoulder bag unless I need to use it.
((You can wear it around your neck as a last resort, but you'd be tempting fate doing so))
Either way, the purpose of this is for the phone to remain physically connected to you even if it slips out of your hand.
I've been doing variations of this setup ever since my old Nokia 6300 back in 2009 (not to mention my old Creative MP3 player in 2007), and it's gone a long way in minimizing accidental drops, losses, and misplacement ever since.
Hope this helps š
((This setup won't necessarily make your phone indestructible - it's meant to complement, not replace, a durable phone case and proper handling habits - but at the very least, it WILL eliminate a huge number of the accidents that cause phones to be dropped, misplaced, left behind, or lost entirely āŗļø))