The answer is, "It depends". Sphagnum is fine for Phals and Dpts if they are getting good light (east window or a foot from a south window that has a white sheer, for example) and you don't water too often. I would either immediately change to bark or if it lives a year, stay with sphagnum.

People new to orchid growing can usually manage bark or bark based mixes better than sphagnum.

Over the last several years, I have tried a number of mediums and plastic/clay pots. I grow my phals under 4 tubes versus 2 tubes for my AVs. The most roots and best leaves have come from using clay pots with "peanuts" in the bottom and sphag amended with some coarse perlite. Great blooms too. If your Dtps came potted in clay with a plastic liner, I would recommend removing the plastic liner ASAP. Use the skewer method to check for moisture in the sphag so you don't overwater. Boyne

Sphag really does hold in moisture. (I've never used it with my gesneriads.) I'm being very careful not to overwater (famous last words), and next year, I will pot up to a clear vessel. This dtps seems very healthy (no plastic liner to kill it off), and I will add two tubes to one of my light stands.

It came with a bamboo stake at the side of the 5.5 inch pot, but I am not sure why, as the two budding and flowering spikes are very upright without support. Is there a reason for this?

The bamboo stake (if it is tall, about 1/2 pencil diameter, and somewhat hollow) was probably potted with the plant "just in case" the spike needed support as it lengthened and became heavy with blooms.

My climate is a bit drier than yours much of the time. My phals actually do noticeably better in sphag, than in a bark heavy mixture. I just repotted three of them because two were failing (leaves losing turgidity) in bark and a third (in bark) looked lackluster.

All three went back into all sphag except for thin layers of granite (for weight) and medium bark at the bottoms of the pots. All are in slotted clear plastic pots. The response was practically immediate and all three plants are now bright green and "smiling."

I second the skewer method suggestion for gauging when to water. One of my phals goes 6 to 10 days between waterings, depending on the weather and the plant's growth cycle. Without skewers I'd have to guess--or stick my finger 3-4" into the middle of the medium. I use the short bamboo barbecue skewers that can be purchased at grocery stores.

Sweetcicely