Can my brother spy on my calls from his cellphone?

Can my brother spy on my calls from his cellphone?

I am 15 and I have a 25-year old boyfriend. My brother doesn't like him very much. My brother told me many times that I must break up with my boyfriend, or he will tell my parents who will never accept puppy love. My brother knows when and where I date my boyfriend. How does he know that? Can he spy on my mobile phones?