In my seat bag so it's there if I need it but otherwise doesn't disturb my ride.

In one of those waterproof cases in my seat bag.

Zip lock bag in shirt pocket for me.

Keep it in my Transit saddle bag. Got caught in a couple of frog stranglers last year and the phone was bone dry.

Rear left jersey pocket. Had it fly out once going down a slight hill because I was messing with it (stupid). Thank God for Lifeproof cases. Phone survived but it banged up the case pretty good.Their warrantee is awesome..

In a Lifeproof case in my left rear jersey pocket. You can't read an iPhone screen in the sun so there's no point in a handlebar mount.

Just in case it never occurred to someone, I had a mystery point impact crack on my phone screen (fortunately just on the tempered glass screen protector). I think it may have been due to stepping off the seat at a light and then pressure or banging it against the nose of the saddle, in my rear pocket. Maybe I leaned back on it, and I've noticed since that I do that now and again. In any event, phone in only the front pocket now and never the rear.

On my handlebars

I've started riding with a small fanny pack. iPhone goes in one pocket, small wallet with ID, a few bucks and credit card goes in another. Also some lip balm and maybe a tiny tube of sunscreen. All tight to my side and under my jersey. I never know it's there.
I hate weight in my jersey pockets. A baggy of dates is the heaviest thing that goes back there and they disappear during my ride!

Keep my iPhone6 in Ziploc in middle jersey pocket. Food in right pocket because I'm right handed and my lucky spare tube in the left pocket.

My Carhartt Parka has a Dry zip pocket on the chest ..

I use a Roadrunner Bags, Mini-burrito handlebar bag for my iPhone and wallet. It is between the drops, easy to hear, and relatively protected be the bars if I fall or if the bike is leaned and then falls. It is a great SMALL handlebar bag which I reinforced with some stiff foam to hold shape and not sag.

I used to keep in in a zipped side jersey pocket, but thought if I seriously fall and needed it to get help, it might have been broken in the fall..

I ride solo most of the time so a phone is a must. Rail trails can take you out in the middle of nowhere it seems. Carry mine in my shorts fromt pocket with zipper closure.

I carry my cell phone in center jersey pocket, even on gravel rides. On some mountain descents, I'm blasting over corse stones and washboard at speed without any suspension at all. Needless to say, its about as rough as it can possibly get, but I've never had anything shake free out my jersey pocket - no worries!
I only use the center pocket out of having a system: Food & gel packs goes in the right pocket; phone or 3rd water bottle in center pocket, while the left pocket is the 'junk drawer' for back-up mini-pump, 2nd spare tube, keys, etc.

Same here... Similar to this one:

Assos Spider Bag. I forget it's there, and good space for neck tube, gillet, arm, and leg warmers too.

https://www.assos.com/spiderbag

this guy mounted on stem, gives me easy access to phone for any needs while riding and holds it pretty securely.

Phone stays on my sling bag strap. Watch gets notifications of texts/emails/phone calls so I can see if it is worth stopping without taking out the phone first. Bluetooth earbuds so I can actually take the call if I want without removing the phone, and can change music (lower volume in traffic and raise on paths). I can read the texts and emails off the watch (and decide whether to stop and respond, activate SIRI to respond over bluetooth, or ignore) and accept calls or decline. Having a phone out just is a flag to getting it ripped off. I have a dedicated bike computer on the bike itself.

I usually keep mine in my rear fender basket, and if it's raining, I'll stash it away in one the rear panniers. If I hear a certain ringtone or text alert, I'll pull over and either check or answer the phone.