Phonosemantic compound. ⻏ represents the meaning and 者 represents the sound. Based on the meaning "large city, capital", which is the meaning when pronounced "dū". When pronounced "dōu", it has the unrelated meaning "all", etymologically related to 多 (many).
都 and 者 don't sound similar in modern Mandarin due to historical phonetic changes. They were more similar
in older Chinese.
Character Evolution
BronzeLate Western Zhou~800 BCBronzeSpring and Autumn771-476 BCBronzeMid Spring and Autumn~600 BCBronzeLate Spring and Autumn~500 BCSealWarring States (Chu)475-221 BCSealWarring States (Chu)475-221 BCSealShuowen~100 ADClericalQin221-206 BCClericalWestern Han202 BC-9 ADClericalWestern Han202 BC-9 ADClericalWestern Han202 BC-9 ADClericalEastern Han25-220 ADClericalEastern Han25-220 ADClericalEastern Han25-220 ADRegularModern