Which is the dominant phase in pteridophytes?

Answer: This is the sporophyte.

The diploid sporophyte is the dominant era in their life cycle. However, fern gametophytes differ from those of seed plants, which are free-living and resemble liverworts.

All pteridophytes do have true generational alternation through which the dominant sporophyte era produces spores via meiosis as well as a free-living gametophyte group produces gametes via mitosis.

Zygote or fertilised egg undergoes mitotic division, forming various segments like roots, stem, sporophyte, and later spores, which are formed via meiosis as well as dispersed, and thus the cycle continues. In pteridophytes, the dominant stage is thus sporophyte.