As you can see, my basilikum plant is quite tall however the leaves are too small. When I bought it a month ago it had really healthy and big leaves. I have cut them to make pesto, and after that they don't grow big enough again.
It looks like its flowering, or about to - cut the plant back by half, you can use what you cut off (including any flowers) for cooking or sprinkling into salads. Give the plant a higher nitrogen than potash fertilizer to encourage more growth. Info here https://www.gardeningknowhow.com/edible/herbs/basil/blooms-on-basil.htm