for an ideologically committed nazi banning the jews from this sort of activity actually makes perfect sense. the nazis who made these policies wanted to transform society into being as anti-semitic as they were and not only that, for there to be no serious opposition left to the regime. they could not manage this overnight and they could not do it by force alone, but they can do it by silencing and stigmatising dissent which may grow into something the regime can't control and by denying any potential form of organisation and any links between jews and non-jews (which in the context of nazi germany is political) however informal it is, an opportunity to start. by making it impossible to be a jew in germany but not only that, to gradually make it impossible to oppose the regime in any way whether that's by bitching about how the telephones are old/broken etc, chatting to your jewish mate on the bus or by taking the piss out of nazi leaders at work or at a party or by printing communist leaflets and planning to assassinate hitler.(and the more these small actions mount up, your views and experiences as you become more aware of issues and more politicised may radicalise you, mean you influence friends etc and lead you into outright hatred of and conflict with the regime, which gives the nazis a real problem if there's more than one of you)
dogs etc are a good way to meet people. not having a phone means that you won't be able to find out about anything like social events that are going on. your kids won't be able to find out about parties etc. the nazis understood this sort of thing, the philosophy was to exclude the jews from the body politic of germany and not let them take part in social life. if you look at guidance for nazi party workers and so on in the 30s its full of stuff complaining about people in pubs bitching about their lives over a pint (and by implication about the regime, if you're complaining that you're working long hours for shit pay or that the roads are in a shit condition and there's dogshit which isnt cleaned etc).
lets say you know a bunch of people through each others dogs and looking after each others dogs when you go away or are working etc. that's how my mum met a lot of her friends when she moved to the area when i was a kid. you might go for walks together with the dogs, you might go out or go for drinks etc. if you're a jew in nazi germany the chances are not all (probably not any) of that group will be ideologically committed nazis. you'll talk to them about work stuff, about local stuff that's happening in the area, and politics might well come into the conversation in some form or other. your situation/others situation almost certainly will if you get to know them enough. there might be a nazi party member in that group but hearing about their friends experience and thinking about their own, at work, their family situation/their mates or whatever - might start to mean that the ideology of the party starts to look increasingly less convincing. you can see it today with people on benefits and opinion polls that mean that as people's experience changes they are increasingly taking a differing view to government lines on welfare.
if this stuff doesn't end up coming up what it will also mean is that the non jewish people who do have dogs or whatever might feel they are less able to talk about their true opinions about the regime (or about stuff thats affecting them on a personal level).
if they did want to help each other out at work or start anything within the community on anything that has the potential of openly challenging the regime (and the nazis transformed pretty much all community organisations even things like chess clubs and flower-arranging societies and so on into organisations that excluded jews and were organised by the party) they will not only not meet potential comrades, the aim is they won't even know that anyone could be remotely sympathetic to what they're trying to do (which could initially just be a non party organised activity, without being "political") at all. it was a deliberately sadistic and nasty element of a programme for the nazification of society, the exclusion of jews and the control of the nazi party over everyone's leisure time and private life, which they hoped would crush organised oppo or stop it before it started.