What is the best formal way to document when you called someone and did not succeed to get hold of him/her?
I am usually documented the case as calling Mr X but no answer, but have the feeling could be much more better than this simple words.
You can note your unanswered call down in several ways, including:
See a previous similar question and the answers to it at:
I called Mr. X but nobody answered.
I called Mr. X but nobody picked up (the phone).
It depends on whether you called the person via a direct-dial phone (one where Mr X would answer himself) of via a telephonist or personal assistant.
For a direct-dial phone, you could say
but I got no answer
but he did not answer
but he did not pick up
If you had to go through and exchange and nobody answered, you could say
I called Mr X's office but I got no answer
I called Mr X's office but nobody answered
If you did speak to somebody else, then it is better to say
but I couldn't get hold of him
or, if the person who offered a reason for his unavailability, you could quote the reason
but he was not at his desk
but he was on holiday
but he was out to lunch