A Ph.D. is a specific type of doctorate degree while a doctorate is an advanced post-secondary degree. A Ph.D. stands for doctor of philosophy, even though Ph.D.s can be earned in subjects that are not a philosophy like hard science. This means that all Ph.D.s are doctorates, but not all doctorates are Ph.Ds.
A Ph degree typically allows the recipient to teach at the highest levels of education. Note that the meaning and significance of a doctorate degree is similar in most countries, but not the exact same. Ph is not necessarily more prestigious than other doctorate degrees like Doctor of Medicine or Doctor of Pharmacy.