The best way I have dealt with these in the past is to tell recruiters and companies that you can only do one date for phone interviews. That way you can plan 4-5 calls in one day.
Far from what recruiters and companies say if they are serious in hiring you they will respect this. They understand you have a job and that whilst you are working for them it is inappropriate for you to be on the phone.
(Doing this is a good way to see if a company really wants you. If you are their ideal candidate they will wait for you to become free).
Failing that you can either arrange first thing in the morning or last thing in the work day. That way you can start a little early or later without causing too much hassle for the recruiter.
Failing that, you need to try and arrange on your lunch breaks (guessing you get an hour or so).