I'd rule with Exploder's post that the Steed isn't real and only has relative substance for the chosen creature. Since AD&D, Phantom Steed has been an Illusion/Shadow spell that states it's a quasi-real creation, versus a Summoning spell that gets you an actual flesh & blood creature. For any other situation than supporting the chosen creature, it's not real. Because it's shadow, it can last just slightly longer than contact illusions, but not much insofar as 1 damage will ruin the spell.They took away the original Mount spell (1st level) in this edition, which previously Conjured a solid horse for the duration, which could pull the wagon. As a side beef, they took away the special movement qualities Phantom Steed would get such as walking over water, making this spell in some ways a Mount with built-in anti-theft device so no one else can drive it.
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