* s /s/ - A voiceless alveolar fricative (like the "s" in "sun").
* k /k/ - A voiceless velar stop (like the "k" in "cat").
* w /w/ - A voiced labiovelar approximant (like the "w" in "we").
* ɛ /ɛ/ - A mid-front unrounded vowel (like the "e" in "bed").
* r /r/ - A voiced alveolar approximant (like the "r" in "red").
So, the phonemes in "square" are /s/ /k/ /w/ /ɛ/ /r/.