Several, but you can easily tell by how much larger the richteri plant is and how much more twisted the petals are. Also, the pearcei/ecuadorense staminode is more triangular whereas the richteri has a reverse elliptic shaped staminode.
This is what Olaf Gruss writes about Phrag. richteri:
"Due to the size of the plant and the length of their sedge-like leaves, plants of P. richteri are easily identified. Their growth habit is very much like that of Phrag. xroethianum, for which they can be mistaken.... The species differs from the other members of the Section Himantopetalum by the following traits: sedge-like leaves up to 70 cm in length; reverse-elliptic staminode with short horn at lower margin; intensely black-brown hairs elsewhere; an occasionally branched inflorescence. The inflorescence can be up to 140 cm tall. In cultivation, these inflorescences can be in flower for up to 18 months, with one to two blooms open at any given time."