Caecilius laid this down on his screen :
Is there a way to convert a three-phase supply to some sort of
redundant single-phase supply?

It should be possible to have (3x) interlocked contactors installed, so
that only one could be active and providing the entire supply, at
anyone time and to the entire building. That should make it possible
for it to sequence, through the phases should one drop out. I have
never seen or heard of it being done, but it is certainly practical to
do.

There would be a short interruption in the supply, during the switch
over.

Best talk to the technical department of your supplier about the
possibilities.

You would still be paying for the 3x supplies, despite only using one
at any time.