Chinese · Pronunciation Guide
pung-yo: a rising first syllable with a strong puff of air and a back nasal, then a weak toneless second.
péngyou
The upward movement is followed by a weightless tail. The neutralisation of 友 is worth noting because the same syllable is a full dipping tone as 有 yǒu, "to have" — so this word contains a syllable that would dip in isolation and is completely flat here. Neutral tone overrides the citation form entirely.
Listen: 朋友
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他是我最好的朋友。
Tā shì wǒ zuì hǎo de péngyou.
He is my best friend.
Listen: 他是我最好的朋友。
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他是我最好的朋友。 keeps hǎo at a full dip because de is toneless — no conversion, even though hǎo dips and there are other dipping tones nearby. Then péng climbs and you fades. The sentence has two toneless syllables, de and you, and they are what keep the rhythm loose rather than marched.
Without a real puff, the p gives béng. The -eng vowel is the other issue: an English "eng" as in "length" is too front, and Mandarin wants the tongue pulled back. And learners restore a dipping tone to you by analogy with 有, producing péng yǒu with two full tones — it should be light enough to be almost inaudible.