My answer is going to be a logical one and I will try and include as many resources as possible but it is mainly logical, also bear in mind that I am not being offensive in my answer and don't intend to be!
The only way I can think of this being permissible is if the employer allows you to have this benefit (Ask your manager or read through the code of conduct in your employment contract)!
If not then you need to bear in mind that stealing is not only considered as unlawfully possessing the physical belongings of others rather it can be in many forms, for example: using the neighbours WIFI network without permission, Now that you have this in mind, I want you to consider the following points:
- Your employer normally pays you to spend your time carrying out your
job role responsibilities and this is normally mentioned within your
contract, therefore by spending your time in carrying out unrelated
tasks that may mean that you are breaking your agreement(contract)
with your employer and gaining income unalwfully!
“and fulfill the promise, surely (every) promise shall be questioned
about.” (Surah al-‘Isrā’, 17:34)
“...and the performers of their promise when they make a promise...”
(Surah al-Baqarah 2:177)
- The phone calls that you are making may be incurring charges to your
employer, which means that someone else is baring the consequences
of your actions! no matter low the cost may be, reffering to the
following hadith:
It was narrated that Abu Hurairah (RA) said: Allah’s Messenger (PBUH)
said, “May Allah curse the thief for he steals an egg and his hand is
cut off, or he steals a rope and his hand is cut off.”
Regarding your last paragraph, Just because something is not specificaly mentioned in the Quran or hadeeth it does not mean that you can assume it is Halal, we thank GOD for his gift of inteligence that we can use our brain to make such decision by the considerations or assesments that we make:
- Is it bringing Harm to others.
- Is it bringing harm to me.
The list can go on and on......
"The halal is clear and the haram is clear, and between them are
matters unclear that are unknown to most people. Whoever is wary of
these unclear matters has absolved his religion and honor. And whoever
indulges in them has indulged in the haram. It is like a shepherd who
herds his sheep too close to preserved sanctuary, and they will
eventually graze in it. Every king has a sanctuary, and the sanctuary
of Allah is what He has made haram. There lies within the body a piece
of flesh. If it is sound, the whole body is sound; and if it is
corrupted, the whole body is corrupted. Verily this piece is the
heart."
I'm sure you don't have this intention in your heart, as you are concerned of it being Haram, but as muslims we always consider the consequences of our actions:
Abu Darda, may Allah be pleased with him, relates that the Holy
Prophet Muhammad, may the peace and blessings of Allah be upon him,
said, “Nothing is heavier in the scales of a believer on the Day of
Judgement than his good behaviour. Allah detests a person who is
obscene and shameless”. (Tirmidhi)
Have a look at point no.10 here
I am no scholar I am just trying to help, I may be wrong but Allah Knows Best!