What is the best free corporate messenger for text and multimedia messaging?

Question

Messengers

I work in a small company where messaging in a WhatsApp group is actively used. Messages, both text and photos, sometimes video. The specifics of the work is such that mobility is an important criterion and all employees are in the above group and there is an active exchange of messages, which is called on the go.
Accordingly, every day each of us receives about 100 multimedia messages, and all of them are stored in the memory of smartphones. It turns out that by the end of the month everyone has a lot of messages in their phones, which negatively affects the performance of the latter - the phones begin to slow down. This forces us to clear the memory of phones and all important information is lost. This made me think, are there any messengers that support the same functions as WhatsApp, but everything is stored on a single, corporate server, and is not saved to the phone?

Answer 1

Slack

Answer 2

Cart?
Rocketchat
Raise your ICQ?)

Answer 3

MyChat. Up to 20 people online - free of charge. Then for the money, but the plus is that you have the server.