No, it's not necessary to be fascinating at or even near 100% of the time. I am boring almost 100% of the time, even to myself, but I still manage to keep myself occupied without going stir crazy.
When you run out of things to say in conversations, try drawing the other people out by asking questions, and then just listening to them speak as they answer the questions. People like a good listener, and you may also come up with other things to say later in the conversation, in response to where the other people have taken the conversation.
As for talking on the phone with people, including girl/boy friends, and family members, you should not call them more than once a day. Even that can be too often. Sometimes two or three times a week is enough. Not that much new stuff happens on a daily basis, to justify more frequent calls. Of course, emergencies, or a need to pick up or be picked up someone, are the exceptions to this rule, but how often do we have real emergencies. On the phone, once you have both run out of things to say it's time to say good bye, and hang up until next time.
Hanging onto a conversation long past it's end is annoying. I can give a personal example. After my mother stopped driving, I became her driver, and care giver. I occasionally had to take her to visit various relatives who lived some distance away. On one trip, we had stayed over one night, so we could have a nice visit with several different relatives in that area. The next day I was ready to start for home at about 5 pm, as I was tired and wanted to get home before it got too late. I told my mother to say her good byes at that time, and said my own then. We didn't get out of there until after 8 pm, and it was late when we got home. It took my mother over 3 hours to say good bye! AAAAAHHHHH!! !! ! Let that be a lesson to you. When the conversation is over, let it go.
My mother passed away over 8 years ago, but even today I still occasionally want to turn to her to tell her about something I've just come across on the news or the I-net that I know would interest her. Unfortunately, that is one conversation that will not come again.
I hope my post helps you. Remember we on the spectrum are all:
A Different Drummer
If a man does not keep pace with his companions,
Perhaps it is because he hears a different drummer.
Let him step to the music which he hears,
However measured or far away.
--Henry David Thoreau