With rotating residential proxies, 5 ports provide 5 separate residential IP connections.
For example:
Port 1 → IP A
Port 2 → IP B
Port 3 → IP C
Port 4 → IP D
Port 5 → IP E
All 5 ports can be used simultaneously, with each port connecting through its own IP.
What about threads?
Threads on a single port are different. Multiple threads can be used simultaneously through the same port and therefore use the same IP.
In short:
5 ports = 5 separate IPs
Multiple threads on 1 port = multiple connections using that port/IP
The IPs can still rotate according to the rotation settings of your residential proxy.