I transitioned from a dedicated GPS unit to a phone app many years ago. I see many advantages to the phone apps. One is trip planning, as you can easily use an online interface to set waypoints, routes, etc. that transfer to your phone before the trip. While in the field you can do everything (and more), like tracking your movements. Some apps have nice features like the ability to share sets of information with others in your party who have the same app.
Differences: you must get used to downloading the relevant maps you need to your phone in advance of a trip so they're usable offline. You must get smart about maintaining your phone battery life in the field: 1) switch to airplane mode (GPS still works) which will ensure several days of use, 2) bring a charging battery to juice back up for longer trips, 3) best to keep the phone from getting too cold, which saps battery (I put mine in my bag with me at night).
There are several good apps. Some have a free version for basic functionality, but full functionality and access to more useful map layers requires a subscription. OnX is good, but the most expensive. GaiaGPS is equally good and more affordable. BaseMap is an up-and-comer and is being aggressive on discounting. There are others, but I'll let those with more experience speak about them.
Overall I prefer the phone apps (I currently rely on GaiaGPS). They are constantly coming out with new, useful map layers and when you get good with them you can do things you cannot do on dedicated GPS devices. For example, upload specialized datasets. Many states have programs where public is granted access to specific private lands, and some departments of F&G provide digital files illustrating those properties that can be uploaded to your phone app.
If you're willing to take the time to learn about them, I think you'll soon become comfortable with them.