Collins has both UK and US versions on the same website, also with IPA symbols and audio files https://www.collinsdictionary.com/ I'd be interested to know from a US teacher how reliable they would consider Collins on the US phonemic transcriptions, as Collins is British. I have found that the free Merriam Webster site has some funny phonemic renditions for some words. In particular, I have noticed that it uses schwas for some stressed vowels. I don't claim any knowledge of the US English IPA subset so I may be missing something.

Merriam-Webster is the standard for the US. Oxford English Dictionary is the standard for the UK. Any good printed dictionary should use IPA symbology for pronunciation. Looking online, I see a dumbed-down version on MW, and none on Oxford. But online you can click the speaker icon and hear it pronounced, so perhaps that's why they don't include it, as least in their free versions. You need at least one good dictionary that has IPA symbols when you are learning a foreign language. ...If you are at the university level, that is.