This is the build that I used to solo Lephantis.

[Energy Siphon] for passive energy [Regen]. Probably a peculiar choice but I found it better than having to rely on energy pads (and because I don't have the Zenurik school available) also because as you travel to the boss room, you should have a lot of energy from either killing things or getting drops from containers and during Phase 1 (and probably 2), you'll regenerate enough energy to use [Rhino]'s other abilities (I always end up with a full energy gauge by the time I finish the fight so maybe taking [Flow] out might be a good idea).

Strength is an obvious thing, but it's necessary for Iron Skin and while we even out on Efficiency from using [Blind Rage] and [Streamline], it's better this than to have [Fleeting Expertise] counteract [Narrow Minded] and have less time to shoot at Lephantis' heads using [Rhino] Stomp.