Like RES-can and Martin, I think #1 sounded considerably better than any literal translation. That is, yes, the word 'reachability' is quite awkward, almost invented, which is why a computer spell check may not even recognize it, even though it's understandable.
If we rethink the question (since so much time has passed anyway), is it really necessary to mention the element of satisfaction? Is there any circumstance we can imagine in which someone would say, Oh, he's very hard to reach by phone, and I'm very satisfied with that?
That's why it makes sense to me simply to ask 'How easy is he to reach by phone?', and just assume that a positive answer will correlate with customer satisfaction.
But if anyone doesn't like using the adjective 'easy to reach,' which is probably what most English speakers would do, then I think it was right for RES-can to suggest 'availability' as a less obscure abstract noun, and it was reasonable for Martin to try 'ease,' though I'm inclined to agree that that phrasing was also too awkward to be very useful.