/dh/ was thought to be an aspirated voiced dental stop, but then some phonologists (e.g., the late Peter Ladefoged) suggest that aspirated voiced stops are really murmured or breathy voice. Your best bet is to find an Indian who speaks Hindi (or one of the other IE northern languages of India) and have them pronounce words, like dharma with the sound in it. The reconstructed PIE phoneme also had some labial feature, hence the little superscript w. There are current controversies on the exact distinctive features of PIE phoneme inventory. The glottalic theory has the traditional (i.e., Neo-Grammmarian) four-way stop series (a la Sanskrit, i.e., p, ph, b, bh) replaced with a series borrowed from the Kartvelian linguistic family (i.e., Georgian, Abkhardian, et al., with glottalized ingressive stops).

NB: the Indo-Iranian languages of India and Pakistan differentiate between dental and retroflex stops. What English grammarians call a dental stop in English is really a alveolar stop, which is closer in sound, and usually transcribed by Indians in loanwords by their retroflex series. The difference is that the tongue touches the teeth in a true dental stop (as the French and other continental Europeans pronounce things), in English the tongue touches the alveolar ridge behind the teeth, and in retroflex, the tongue is curled up and touches the palate immediately behind the alveolar ridge.

Ceci n'est pas un seing.