Don't. Just don't. Please.
Just a few weeks of usage can cause dependence. It is notorious for causing compulsive redosing. Withdrawal can make you unable to sleep for days, with lingering effects like panic attacks and anhedonia for weeks and weeks. Withdrawal from larger quantities can cause auditory and visual hallucinations and seizures and can even KILL you. Avoiding serious symptoms requires an excruciating taper that can take months. The effects of long term abuse are poorly understood.
"But it's totally legal, and with responsible dosing can be a potent nootropic. I'm not a drug addict, I'm a biohacker. I'm not after a high."
Yeah, That was my thinking too, and in hindsight that was immensely stupid. Please just look at r/quittingphenibut before doing anything.
Be kind to your GABA receptors.