Dealing with Jekyll and Hyde
Most of us have worked with someone who acts respectful and collaborative when the manager is around but completely changes their behavior the minute you're alone.
A disingenuous colleague can be very frustrating and unproductive, and it is tempting to tell your manager about the inconsistent behavior. However, talking poorly about the person will often backfire, and you will be the one to look bad. Badmouthing the person to other colleagues or rolling your eyes when they speak will only make you look unscrupulous.
As hard as it may be, take the high road and stay positive. Keep your relationship and tone cordial and constructive, focusing on the work you need to get done together, not on their behavior. Good leaders aren't fooled over the long run, and senior leaders will notice people who are truly collaborative and supportive of others.