Ok, so, airplanes are difficult! @Hutima is correct that many of them block GPS signal almost completely.
Boeing airplanes are the most problematic, in my experience (or perhaps it’s just the 787), while Airbus planes are much easier to maintain GPS in.
In an Airbus airplane as long as you’ve got the phone within 30-60 centimetres of the window it can usually hold a GPS signal and record the flight correctly. If you have your table out, keeping the phone on or above the table will usually get you a reliable recording throughout. If you have your phone below the table your odds of success diminish significantly. If your phone loses GPS signal it will be necessary to hold it near the window for a minute or so until it picks up enough satellites again.
On Boeing flights however I’ve had almost universal failure. Signal loss is almost permanent and unrecoverable, despite holding the phone right up against the window for extended periods.
Here’s examples of recent Airbus and Boeing flights:
In the Airbus recording you can see the speed data blipped a bunch of times, meaning that signal was lost, which would have been times when I put the phone down on my lap or on the empty middle seat away from the window. The signal would then have picked up again once I was handling the phone above my lap, near enough to the window.
In the Boeing recording it’s simply a 100% loss throughout, and nothing I did could save it. Something about the 787 really doesn’t work nicely with GPS.
Airplane Mode won’t hurt recording, thankfully. Inside buildings on the ground, Airplane Mode will hinder location data accuracy, because when you’re inside buildings without line-of-sight out windows your phone will use cell tower triangulation to help it get a fix. But when inside an airplane cell towers are of no help, and likewise wifi hotspot triangulation is no use, so the phone has to rely purely on GPS/GNSS signal. That means it needs to be able to maintain constant line-of-sight to enough satellites, otherwise it will lose your location completely.
Unfortunately not. Though perhaps if some flight tracking service supports exporting of a specific flight’s tracking data to GPX or similar, it could be imported into Arc. But that would be quite a fiddly process.
The two main takeaways: 1) Keep your phone close enough to the window, eg within 30-60 centimetres and without its view out the window blocked. 2) Avoid Boeing 787s.