The law states that an international non-resident hunter must be accompanied by a licensed PH, and hunting with a registered outfitter. That being said, the interpretation of what "accompanied" means can be pretty loose with some outfitters an PHs. I am aware of many instances where the hunter was dropped off by the PH to hunt alone. With no real presence of the law in existence in the bush on private land, it's nearly impossible to enforce. It probably happens a lot.
Regardless of the legalities, there are many good reasons why a PH should accompany any hunter into the bush with safety being paramount. Secondly, any hunter who is not familiar with African game will find it very difficult, if not impossible to properly judge the animals for age and trophy quality. It is for that reason alone that most any reputable PH or outfitter would insist on being with the hunter to make those judgements. Unless you are very familiar with the properties, the predators, and the game animals, I personally do not recommend hunting by yourself in Africa even if it is permitted by the PH/Outfitter.