So, I'm going to start with the phonology of the earliest attested phase of the language, termed Ancient Methinat, spoken around 2100 BC. The most major phonological developments from PIE include palatalisation of the front dorsals, resolution of the syllabic consonants (including laryngeals), fricativisation of the aspirates, merger of the laryngeals, and loss of labialisation. All this change produces the following inventory:

		Labial	Dental	Alveolar	Palatal	Velar	Glottal
Stop	Unvoiced	p	t		c	k	ʔ
	Voiced	b	d		ɟ <j>	g
Fricative		f	θ <þ>	s	ç <ś>	x	h
Nasal		m	n
Approximant		w	l	r	j <y>

	Front	Central	Back
High	i		u
Mid	e	ə	o
Low		a

Stressed vowels are marked with an acute, long vowels with a macron.

The inherited stress system is virtually intact by this point, though it gets reorganised within several hundred years. The vowel ə has its locus in syllabic sonorants, but spread to all zero-grade root syllables, similarly to Tocharian. This means the primary ablaut system is o ~ e ~ ə. There are a few minor synchronic rules that should be mentioned: TsT clusters (T is any stop) are regularly reduced to sT (except old labiovelars reduce to w); NB clusters (B is a voiced stop) assimilate to NN. h and s are also in a mostly complementary distribution in inherited words, with h appearing word-initially and intervocalically.