A high daily dose of an opioid such as oxycodone is not enough to label a patient an addict. Addiction is defined by craving, uncontrolled or compulsive use. The person continues to use the drug despite harm. It's rare to develop the disease of addiction if a person has no risk factors.
It's more likely your father has a physical dependence. Dependence occurs in everyone on opioids. This happens when you take them regularly for more than two to three weeks. Physical dependence does not mean the person is addicted. It just means that the body has become used to the drug. If the person stops taking the drug suddenly, then symptoms of withdrawal may occur.
There is another concept you should understand about oxycodone. Patients can develop tolerance to the drug. Tolerance means the person needs more drug to get the same amount of pain relief. Tolerance is not the same as addiction.
Not everyone develops tolerance to pain relief. If your father is starting to develop tolerance, there are ways to deal with it. His doctor may want to switch to a different drug. Or sometimes treating other conditions such as depression and anxiety helps.
Adding a non-opioid drug can offer some extra pain relief without increasing the addictive effects. The best approach depends on each patient's situation. Talk with your father about your concerns. He may have the same worry about becoming an addict. His physician should be able to give you an idea of what to look for and how to avoid addiction.