Phonosemantic compound. 刂 represents the meaning and 戈 represents the sound. In simplified Chinese 划 is also used to mean "cut, delimit, draw", while in traditional Chinese this meaning is written with a separate character 劃.
划 and 戈 don't sound similar in modern Mandarin due to historical phonetic changes. They were more similar in older Chinese.划 /*C.[g]ʷˤraj (?)/ 戈 /*kʷˤaj/