According to the rules of the Suffolk League (and the Bury Area League), your opponent loses the game. You get the full point, unless you have insufficient mating material, when the result would be ½ - 0.
But in reality, what actually does happen? I've been in a couple of situations in recent league matches where my opponent's phone has rung. In one, he casually lent over to his jacket which was hanging on his chair, turned the phone off and resumed thinking about his next move. I was in a quandary; should I claim the game, or say something, or what? On the other occasion my opponent was more generous. Admitting his fault, he asked, "I suppose that means I lose the game?" It was easy for me to say, yes, I'm afraid it does. And that was that; 1 - 0 to me. But returning to the first instance, it's embarrassing to have to tell your opponent that he has lost the game, which is why I kept quiet (fortunately, I went on to win, anyway). It's absolutely clear from the rules that it's a loss for the person whose phone has made a noise and he/she should resign on the spot.
OK, that's the law according to FIDE, which both local leagues have incorporated into their rules. But I'm going to suggest something rather different and would welcome opinions from other local players.
Whilst in a tournament, where there is a controller/arbiter, the decision is clear: the player loses. But in a local league, where we all know each other as friends, it does seem a bit brutal to have to concede the game. I suggest that if it occurs in a Suffolk League match, or any of the competitions organised by the SCCA, then the game continues, but that person is banned from playing in the next match for which he would normally be selected. So a regular in a team would miss the next match for that team.
That's it; no loss of game, but perhaps a slight loss of face. "Why aren't you playing in the match tonight?" "Oh, in the last match I forgot to switch off my phone and it rung, so I've been banned for this match".
How does that sound to you? Let's hear your views. If this idea is generally supported, it could be put as a proposal to the Suffolk AGM on 10 June.