The easiest (and cheapest) way to couple powerline phases for Insteon is probably by installing a dual band lamplinc module on each phase of your breaker panel, and in somewhat close proximity to each other (ideally in the same room). They're plug in modules, so easy to move around. However if you have lots of other dual band devices, such as wall switches, then this will often be sufficient too. A setup with just a few devices is less reliable than one with many, as is the case with other mesh network topologies.
Yes, the 2477S is dual band (has both powerline and rf communications). The dual band technology is a big part of Insteon's reliability. If the only Insteon device(s) you have are wall switches, then trying things like moving it closer to the PLM will be difficult. Tell us what you have exactly, and how they're laid out.
I have a mid size setup (about 35 to 40 Insteon devices) and is a mix of dual band and powerline only devices (I bought several lots of used devices). I'd say about 2/3rds of them are dual band. I consciously set them up to have dual band switches in at least every part of the house. Some devices are also rf only, such as the battery powered Triggerlinc magentic door detectors, mini remotes, and the thermostats.