Let $\phi$ be a Drinfeld module over function field $K$. It is known that if rank of $\phi$ is 1, then it is isomorphic to one defined over $O_K$. Is it true that if rank of $\phi$ is arbitrary, then it is isogenous to one defined over $O_K$?

Let $\phi$ be a Drinfeld module over a function field $K$. It is known that if the rank of $\phi$ is 1, then it is isomorphic over $K$ to one defined over $O_K$. Is it true that if the rank of $\phi$ is arbitrary, then it is isogenous over $K$ to one defined over $O_K$?