Phone as an modem sharing connection to old laptop that works as a router does basic mining very well too, I have tried.
Question remains, if 100Mbps router costs $40 and 1Gbps router $50, what is the reason to save that $10?
That is right. If the latency of the 1Gbps is lower than the 100Mbps, then it is OK to buy the faster one.
When the latency in both cases is measured in MICROseconds as a general rule, it's NOT AN ISSUE.