I only know my mobile phone number, but I don't know my boss's last name. Should I call someone to ask about the recruitment? how

You can call it a leader, a boss or hello.

I want to ask, are you still hiring? If you have a mobile phone number, you can choose to call the other party during office hours. It doesn't matter if you don't know each other's last name. You can just ask, "Boss, are you still hiring?" Or "hello, leader, are you still hiring?"

Finding a job is a two-way choice. You can take the initiative to choose a job, or you can let your work unit choose you. We must study more in the face of the workplace.