The obvious app is Strava but even though the typical smartphone might have a bigger screen and faster CPU, it's hard to compete with devices that are optimized for cycling. I don't think Garmin and Wahoo have anything to worry about.

I think Strava will connect to HR. I know it will connect to Power as I tested it once buying a used Stages a whiles back (in person) to see if it was still working. But if you have Ant+ stuff then you'd also require and Ant+ stick. Or maybe MapMyRide?

But, ymmv because battery life in GPS mode sucks on most phones, you'll probably be lucky to get more than 2-3 hours out of it before you run out of juice. If you don't have unlimited data then you are also screwed on the recording data because you'll probably run out very quickly.

Heck, my newest phone is my work phone (Galaxy S9) and that battery life sucks. Battery will drain to 0% if I leave it over the weekend unused (just on and receiving email) at times starting on mid-day Friday or earlier.

Ipbike if you have an Android phone and Ant+ sensors. Battery life is an issue, I only use it if I've forgotten my bike computer, so I've never used it more than an hour and a half.

I'm going to throw this out there, if you replace a garmin/wahoo with your phone, I assume your going to be putting your phone on your handlebars so you can see the data. Do you really want to put your emergency communication device front and center of a potential crash?

This (not all Android phones have native ANT+ support, but pretty much all can use USB-OTG plus a dongle to get support). You're best off using this as a data recorder and having your screen off, since GPS + a bright enough screen to see with the OLED screens most phones use these days eats battery super fast.

Reasons why Garmin doesn't have to (fully) fear the phone as a bike computer replacement
- Battery life
- Outdoor screen optimization (OLED screens used on phones need to crank the brightness to overcome the sun)
- GPS accuracy at speed in the wild (phones work well when moving at slower speeds and can also use WiFi data to enhance their positioning)
- Durability (weatherproofing, drop resistance)
- Cost vs placement (new high-end phones are close to 1k and mounting one on your handlebars is a precarious spot during a crash)

That being said, it does seem like there is more price sensitivity on the bike computer than watch front. e.g., the Edge 530 launched over 3 years after the 520 at the same price and has a lot more features - basically up to the 8xx series, vs the 920 to 935 jumped $50 and the 945 jumped another $100 over a slightly longer overall timeline.

I kept an old phone and use it at times. Put it in a waterproof/shockproof case. I actually like the phone for following a route better than my bike computer, especially mountain biking.

Of all the apps, I've found Wahoo's to be the best (it will then let you share to TP, Strava, etc.). It's free, and works with any BT sensors.

Notes and Commercial Plug:
If you want to keep your phone in your pocket (and save battery life), I'd recommend a Wahoo RFLKT. It's basically a "dumb terminal" that bluetooths to your phone and shows all the values (speed, power, cadence, hr, etc., etc.) from the app. I don't think they make them any more (they were more of a necessity in the iPhone6 days where your phone would die in 2hrs with screen and GPS on). I have an old one I no longer use that I'd let go cheap.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)