play sth by ear

/plˈeɪ ˌɛstˌiːˈeɪtʃ baɪ ˈiə/

/plˈeɪ ˌɛstˌiːˈeɪtʃ baɪ ˈɪɹ/

to play sth by ear

to be able to play music by hearing it instead of reading it

to decide on one's course of action as a situation develops instead preparing or planning one's actions