What this says about his philosophy probably depends significantly on how irritating you find it.
That said, it's worth noting that it's certainly not that he doesn't care about the privacy of others. I had to pull him away from lecturing innocent bystanders about paying at the grocery store with CCs.
I have his book, and his practicality has always struck me, juxtaposed against his idealism, it just looks really strange. You don't expect to see him doing certain things. But then you ask him about it and he's got a perfectly reasonable explanation. I've read so many stories about people that have interacted with him in precisely that way.
Both Stallman and the Amish take a very long view. Every decision they make carries the entire weight of the future and must be considered in that light. They both fight against the constant march of modernity. They are institution builders.
Otherwise it's just crap stuffed up in your own head.
For him, it is more irritating to live in a world that thinks it is okay to regularly violate people through crossing boundaries of what they consider personal information. For you, it is more irritating to go into a public space and have to deal with other people's opinions.
Everyone is fine with things as long as things are perfect for them. But you can't just wear blinders over your eyes when other people are obviously suffering, and just because you can't empathize with why those people are suffering doesn't make their suffering any less deserving or worthy of understanding, lest you expect the world to treat your suffering in the same cold, disconnected, blinded manner.
I'm sorry he embarrassed you, he would probably embarrass me too in the day to day minutia. But I absolutely stand by him mentally, because I believe and value the world he believes in and values. In theory everything is honky-dory. In practice, society and the individual actually has to deal with problems as they exist. Otherwise they fester and turn into more difficult problems that take a long, long time to understand - some of which are very very difficult to understand after enough time has passed and enough damage has been done.
I can't tell you how much I as a programmer and computer scientist, how much I have benefited from the movement that came from Richard Stallman. I can't tell you how much my mind has benefited from it. I don't care that his actions contradict his core philosophy. They are attempts at connecting a gap between theory and real life.
If the source of code was as privatized and closed as some kinds of knowledge can be, I'd be nothing. I consider it a privilege to share an existence with a person who has helped shaped the world in that way, no matter how annoying or crotchety or irritating he may become. There is always a difference between the ideal a person represents and the person they are. It comes at a high cost to be a public figure, but some people see the value of the world they want to create for everyone to be worth more than that - and maybe that's what the people around him who allow him to use their cellphones see too.
The thing I found irritating was RMS constantly borrowing my phone (and having to help him use it each time...). He can have whatever opinions he wants.
To answer seriously, however, the largest effect of reduced cell phone use would be that automobiles would be much safer, for their passengers and for everyone else.
Listening to RMS would mean that if you do carry a mobile device, that it would use entirely free software including all drivers and bootloaders, that it only communicates with other hardware running entirely free software (i.e. only basetowers or wifi routers running free software), and that all the internet services accessed ran entirely free software (e.g. private email servers instead of gmail, pump.io & GNU social instead of twitter & facebook, mediagoblin instead of youtube, wikipedia, yacy or some other free software for search, etc.
Stallman is taking a stand here. We might think that he is a dangerous extremist for his actions and stances (Not using proprietary software, mobile phones, javascript-enabled websites). But what he is actually doing is sacrificing his life to make his points (which are for the most part completely valid). I would guess, even he knows that most of his ideals are impractical in today's world, but he is walking the walk and planting the flag firmly, saying this is "How thing should be".
The difference between a crackpot and a visionary is that what the visionary says make more sense as time passes. IMO, Stallman's track record is infallible in this regard.