Would you say that all your "interruption slots" are taken by a need to look at a phone or particular app? Aren't there still situations where you break your current focus (be it something important or just waiting in the elevator) with an actual thought not related to the phone?
I agree that position I've presented probably stands to some degree on the assumption that there still is a noticeable amount of non phone related interruptions of one's thought patterns. Otherwise my claim of equivalence would be stronger and require more arguments that I have at the moment.
From my personal experience (n=1) it's exactly the case - sometimes it's a phone, sometimes not, so that clearly directs my judgement. OTOH I find it unlikely that this is particularly atypical.