Communication with a student pursuing the bachelor's thesis
Giving your personal phone number to a Bachelor's Thesis student will allow the student to contact you at inconvenient hours or during your free time. This is the main reason why people do not give their private phone numbers at work (neither to students nor to their boss).

If you are fine with this, there is probably not going to be any other major consequence. The student is not going to think less of you (on the contrary, they will appreciate it), and others (colleagues, boss...) will probably be indifferent. In the end, it is your choice how you want to communicate with your students.