わたしの ボスから ききました。(WATASHI NO BOSU KARA KIKIMASHITA) わたしの ボスに ききました。(WATASHI NO BOSU NI KIKIMASHITA) = I heard (it) from my boss.
こばやしさんに ききました。(KOBAYASHI SAN NI KIKIMASHITA) こばやしさんから ききました。(KOBAYASHI SAN KARA KIKIMASHITA) = I heard (it) from Kobayashi-san.
You can use either one of the two. Both particles mean “from” in the above sentences.
However, the verb きく (KIKU) has a few meanings (to listen, to hear and to ask). So it may get confusing and hard to figure out if it means “to hear” or “to ask” sometimes. For example;
•A starts talking to B all of a sudden.
A:きょう、わたしのボスに ききました。 (KYOU, WATASHI NO BOSU NI KIKIMASHITA) = I heard (something) from my boss today.
B:なにを ききましたか。(NANI O KIKIMASHITAKA) = What did you ask (him)?
Since B (a listener) didn’t know what A was talking about (no context), B misunderstood and thought A said “I asked my boss (about something) today.” If A said わたしのボスからききました instead, B would understand fully what A was saying.
(someone) に きく。＝ to ask (someone), to hear from (someone) (someone) から きく。 = to hear from (someone) (something)を きく。= to hear/listen to (music, voice, sound etc.)
If you want to make it clear that you are talking about what you have “heard”, から (KARA/from) would be the best option.
As for your second question, you have to say;
いま、おとうさんから でんわが きています。(IMA, OTOUSAN KARA DENWA GA KITEIMASU) = I am getting a call from my father now.