Synthesizer V build 14 let's you go to View > Open Phoneme Viewer to see the possible ARPABET phonemes, but I didn't like how it was organized (it's in alphabetical order and jumbles up vowels and consonants), so I made my own chart.
If you notice any mistakes or have suggestions for the chart, feel free to say so. There were some questionable phonemes, like ARPABET "aa" (IPA "ɑ") doesn't appear to have a Vocaloid equivalent. And then there are "dr" and "tr" in Synth V, which doesn't even have an official ARPABET version and therefore no X-SAMPA version, so I just left them as N/A.