Depends on the use case an server.
Google and facebook do not yet have public servers. You want a trudtworthy server such that noone abuses your metadata like the time of sending a message.
It’s very useful for companies like email but for real time communication. I’d prefer matrix over most other forms. In many companies and agencies matrix is getting introduced these days.
It’s not anonymuous just like signal isn’t perfectly anonymuous.
As soon as you share the into with a potential employer that it is you, you lose the privacy. You have to assume it’s publicly known. It’s not worth the effort.
If you do your research everyone knows you spend most of your day researching anyway. At least your supervisor will know who you are. You will want to talk to others and tell them “I’m currently research xy. I wrote this idea, what do you think about it?” Etc.
You should do the phd because you are intrested in the topic, not to gain some degree.
You can write your good papers as an anonymuous person. If they are very good, people would cite you. People will want to invite you.
I’ve got an android