First of all, the standard pronunciation of/_/is "er" in both English and American English, but the tongue position of American English sounds higher, so sometimes it may sound a bit like clothes, but strict native speakers of American English still pronounce er.

Second, the /I:/ with a long sound symbol is the familiar long-sleeved sound. And /i/, without a long sound symbol, is naturally a shortened garment sound, that is, the pronunciation is not as long as the garment.