Is what the husband does—joking, laughing, and phone calls with his female colleagues at work, and looking unlawfully at their bodies—considered marital infidelity?

Deliberately looking at non-mahram women is forbidden (haram). What leads to it, such as conversation, familiarity, or smiling, is also forbidden. Therefore, it is necessary to cut off relationships with girls and limit communication with them to what is absolutely necessary, avoiding private seclusion with them (khalwa) or looking at them.