The phrase "a stage upon" is correct and usable in written English.
It can be used to describe a specific phase or level in a process or development, often in a metaphorical sense.
Example: "We are currently at a stage upon which we can evaluate the project's success."
Alternatives: "a phase in which" or "a level at which".
The festival guests used the steps as seating, and the mooring became a stage upon which we gave out the awards.
Humans performing like machines; inert materials behaving like nature — Biddle's process is a stage upon which little dramas of creation unfold.
The Hemingway-Fitzgerald generation and its literary successors have tended to treat the world, when they did treat it, as a stage upon which Americans could be more heroically or plangently themselves, or (following the generations down to our day) introspectively, narcotically or psychotically themselves.
People fell in love with him when they met him, he says, but the red carpet wasn't a stage upon which he felt comfortable.
For over 40 years, the annual juried exhibition sponsored by Brand Library Associates has been a stage upon which artists from across the nation have exhibited their work.
Mountains, rivers, and forests are not perceived as being inanimate, as mere props on a stage upon which the human drama unfolds.
Three actors and a percussionist occupy a spare stage upon which a circle has been drawn in sand.
The majority of the hemisphere is simply a stage set, upon which US citizens can pleasurably fantasize about losing their souls or finding them.
"This was a time-capsule world: a dim stage upon which people raged, spilled blood, experienced visions and ecstasies," Kaplan wrote in 1993.
The blonde had transferred her digital fury to the downstairs piano, a white lacquer job on a tiny stage, upon which she set about marauding "Heart and Soul".
"A positive and appreciative approach always sets a better stage upon which your drama can be played out," wrote Hoover in an email.
