[Phantasma Prime] has mildly stronger critical stats than base [Phantasma], but they are a builder's trap, as they are not actually high enough to warrant modding for.

This build opts for the convenience of viral damage on-weapon rather than priming for it externally. This can make the weapon especially effective in middle content just as starting level Steel Path, or if the time saved from viral priming is more than the +50% higher potential with a viral-less build.

I guess other information about beams: [Phantasma] is a unique multibeam with 5 + 1 beams in one. Unlike traditional shotguns, these beams combine their instances when hitting a single target, adding damage together into a single instance, as well as adding their status chances together on this single instance. The result is a base of 90 damage with 22.2% x 6 = 133.2% status chance at base. Other shotguns do NOT multiply status x multishot in this way.

This means that +multishot bonuses has obscenely high value pertaining to status damage such as Electric. It increases the damage output of the weapon AND the total status chance of that instance, having a squared effect on status damage. This is why status damage is the explicit focus of the weapon, and why the critical improvement at base needs to do better to warrant modding. If beams ever get fixed, this may change.

Rivens replace Shotgun Barrage. Their desired stats in order are: Multishot -> Fire Rate/(Faction) -> Electric -> Damage/Status chance. -Impact can have a subtle positive effect, but it is marginal. If impact is completely removed, you lose 80% damage. Status Chance has the highest potential damage ceiling with priming involved, but Electric has potential to slot into this more convenient viral build and has more up-front damage, at the cost of a slightly lower ceiling.

Currently the weapon suffers from an inferior disposition to the base Phantasma. With the godliest roll of MS FR SC -imp, the weapon needs 1.0 disposition to surpass the base [Phantasma] which currently has 1.05 disposition. With lesser riven stats and grades, the slightly improved base of [Phantasma Prime] can pull it ahead at a disposition of 0.95. If your riven is removing all of normal [Phantasma]'s Impact, then Prime wins at as low as 0.85 dispo.

Exilus up to you, not super critical.

Deadhead is an alternative. Uptime suffers from reload loss, but Electricity procs will get 1.3 x 1.3 = 1.69x damage on headprocs. Just aim a little higher. Although Electricity ticks itself may not be able to proc the damage bonus, in which case it's unslottable.