Is necessary to assign the SPA-841 Port 5065 or can use 5060?
There is generally no need to modify any of these settings. Your Asterisk can distinguish between 5060 of your 2100 and 5060 of your 841 because they have different IP addresses. It’s just the same as the 20 PCs all doing web browsing simultaneously all using port 80. The router keeps track of all of this. That’s its job. So, don’t worry about it unless something doesn’t work.