I'm an android user, but I hope this is still helpful.
The Reader is very basic, not unlike comparing a Nokia phone from 15yrs ago with a smart phone today. I've used 3 L2 readers since 3 Feb, all behaved similarly. Using it to put data in, eg insulin doses and carbs, is crude and clumsy with the touch screen frequently unresponsive. My smartphone with the Librelink app is much more sophisticated for data entry and provides reasonable reports, even before looking at the reports in the cloud on Libreview. Data from the Reader can only be transferred to Libreview by a connection cable and a PC, whereas from my phone it goes automatically by WiFi, once I'd set up my Libreview account.
BUT, despite these negatives, I have tried using the phone only and reverted back to using both the Reader and phone in parallel - for the ALARMS. It is true, there is the nuisance of carrying an extra device; but if I'm in the garden or with kith and kin, I don't need the phone, just something that will alert me when I'm heading to hypo terrain. For this purpose the Reader is light and convenient; I've got an improvised pouch on a lanyard for when my pockets are inconvenient carriers. Once the alarm goes the display is immediate and clear and I can decide what response I need to take quickly. On my phone (perhaps my smartphone skills are limited) I find I need to get the phone out, wake it up, etc and generally it's a much slower process. I use the phone fully for putting in data and remarks, or logbook notes, as memory joggers when I'm studying Libreview.
Also, I found on my 3+ yr old Samsung A5, that various notifications from other apps were interfering with the alarms, often disconnecting the alarm, which I didn't know until the next time I looked at the awake phone. This happened 3 times in the early hours and I'd sleep through bad lows, which defeated the purpose of wearing a sensor. I eventually removed all notifications except Llibre 2, but I felt uncomfortable about isolating potential incoming notifications. I might reason that I used to manage without such smartphone "conveniences", but the modern world is steadily expecting me to pick up notifications promptly and more and more agencies are assuming that I will see these promptly. The neutralisation of alarms might not be a problem on a newish iPhone.
The Reader alarm signals are also fixed and very basic, I can improve the ring tone selection on my phone - but this shortcoming is not a big issue for me. The main thing is that the Libre will only send alarms to one device, so if you want that to be the Reader it must be activated BEFORE the phone.
Overall, I'd suggest activate the Reader first and use it solely for the alarm functions, accepting that you always need to keep it close; then activate your phone and use that for data input and review of Librelink reports - knowing there is no harm if you aren't in the same room as your phone every minute of 24 hours a day. You can try something different, eg phone only, when you change the sensor after 14 days.