Final answer:
The phrasal verb 'dress up' refers to putting on more formal and elegant attire, which is often expected in professional settings until one becomes familiar with the workplace's dress code.
Step-by-step explanation:
The phrasal verb that means to put on clothes that are more formal and elegant than those you usually wear is b) Dress up. In many professional settings, there is an expectation to dress formally at least until you become accustomed to the workplace's attire standards. Adapting to the dress code is important as it not only reflects personal professionalism but also aligns with company culture and workplace expectations.