I will try to give some insight about this. I think it is a hybird:
Here is the description of Dend. aphyllum (aka. Dend. pierardii) and Dend. primulinum fro the Dendrobium bible by Baker and Baker:
Dend. aphyllum (aka. Dend pierardii): 1-3 flowers per inflorescence. Bloom is 3-5 cm (1-2i inch) and lasts about 3 weeks. Strong violet fragrance. The sepals and petals may be nearly white or have a pale, rosy-mauve tint with magenta at the tips. The lip is cream to bright primrose yellow with purple veins or markngs at the base and a grenish yellow disk. The lip is densely hairy on both surfaces. It appears funnel-shaped, but it is nearly round when spread. The lip is highly variable in color, size, and shape.
Dend. primulinum: 1-2 flowers per inflorescence. The flowers are 2-3 inch (4-8cm) across. The narrow sepals and petals may be purple, mauve, rose-pink, or white with rose at the tip. They contract sharply with the yellow lip. The large, downy lip is shaped like a flared trumpet with a fringe along the margin. It may be pale cream-yellow or bright primrose-yellow. The throat is tinged with dark red or purple near the base. The strong fragrance reminds some of cowslips. The blooms last 1-2 weeks.
If I remember correctly, for Dend. primulinum, the Laos form has the really dark yellow lip.
Thank you for all the details. I will label as a hybrid of ?
I am unable to ask the place purchased in that I have had for at least 15 years and memory fails me as to which purchased from of the many greenhouses and orchid sales I visit.