The phase of the cell cycle one would expect triploid cells to be unable to complete would be Meiosis I.
During meiosis I, homologous chromosomes pair up to form bivalents or tetrads. This means that for a triploid cell, one chromosome will not have a partner to pair with.
The existence of an unpaired chromosome after the pairing of homologous chromosomes will make the remaining processes of meiosis I likely impossible.
More on meiosis I can be found here: https://brainly.com/question/2095046?referrer=searchResults
