What is the ruling on exchanging phrases such as "How are you?" between male and female colleagues at work?

The fundamental principle is that women should work in environments where they do not mix with men. However, if necessity dictates that both genders work in the same place, then interaction between them must be limited to what is strictly necessary. As for speaking with a non-mahram woman without need, it is a precursor to what is unlawful, as stated by the esteemed scholar Al-Khadimi. Furthermore, giving salutations (salam) to a non-mahram woman is not permissible if there is a fear of temptation (fitna), as indicated by Ibn Hajar.