Yes, most Chinese characters are phono-semantic compounds.[0] However, this makes most sense in the original Old Chinese[1] phonology, where the forms were taking place.
For example,
偒 was pronounced /*l̥ʰaːŋʔ/ and 陽 was pronounced /*laŋ/, but the modern pronunciations are tǎng (/tʰɑŋ²¹⁴/) and yáng (/jɑŋ³⁵/) respectively. So the phonetic part 昜 /*laŋ/ no longer consistently represents that sound, although in this case the final -aŋ is still present.
And as for sounds that were present in Old Chinese but not in Middle Chinese and Mandarin, like [2] 巽 was pronounced /*sqʰuːns/, now xùn (/ɕyn⁵¹/), they underwent a series of regular sound shifts that make them sound quite different when used in characters in Mandarin.
Also, Old Chinese was not a tonal language, tones first appeared in Middle Chinese, which the modern system derives from (with changes). Tones never had a chance to appear in writing.
[0] https://en.wikipedia.org/wiki/Chinese_character_classificati...
[1] https://en.wikipedia.org/wiki/Old_Chinese
[2] https://en.wiktionary.org/wiki/%E5%B7%BD