Tongue and jaw position move the first two formant frequencies

Evidence

Roughly, the first formant is raised in frequency, from about 300 Hz to 700 Hz, by opening the mouth and lowering the tongue; the second formant is raised in frequency, from roughly 700 Hz to 2300 Hz, by moving the tongue forward. — Eric J. Heller, Why You Hear What You Hear- An…, 1680