Very much. Phone GPS chips vary & the materials in the case affect things. Some phones have barometers too (not many) which give you more accurate altitude, though Strava corrects this online, eventually.
Most phones these days have Assisted GPS also which uses the network to get a quicker lock (basically downloads a list of where the satellites are, which otherwise takes a long time just via GPS). Doesn’t affect the positioning directly, but can affect the position at the start of a ride if you have no phone signal and it hasn’t locked on yet.
Not to go too technical, but GPS chips in phones often have and in built filter for low speeds to filter out fluctuations. This is done to improve accuracy for driving navigation, but makes tracking when walking and cycling a bit poor. This is separate from any auto-pause feature that GPS apps use, though Strava doesn’t use auto-pause itself (but is screwed up by people using other apps to track or a Garmin and have the pause turned on).
Sampling of the GPS signal can be out of sync with your riding buddies also, and yes tree cover and all kinds of things can make the two not equal. I frequently get segments matched that a friend doesn’t and vice versa, or I get random spikes at times. Though I use my old Nokia phone to track using Endomondo (auto-pause disabled) and upload the GPX to Strava, as my regular Galaxy S2 phone is very rubbish at GPS, and the Strava app produces big errors in the track. Not to mention rubbish battery life.
I’ll get round to getting a Garmin at some point though. One day.
