All the different components which make up the processor have to be condensed…

Concept

A System on a Chip (SoC) is a single integrated circuit that packages together the major functional blocks of a computing system — the processor core, memory controllers, input/output interfaces, and often graphics or signal-processing units — instead of building each block as a separate discrete component on a circuit board. This design approach lets an entire computer system fit onto one piece of silicon, in a very small physical footprint.

Application

The question describes exactly this situation: every separate component that makes up the processor has to be condensed onto one chip so that the whole assembly is small enough to fit inside a smartphone. Condensing all of a processor's constituent components into a single chip is the defining feature of a System on a Chip, so the blank is filled by 'System on a chip'.

Contrast

• Touch on a chip is not a term about processor integration at all — it names touchscreen sensing technology.

• Memory on a chip describes only storage (RAM/ROM) built into a chip, not the processor's other components.

• Processor on a chip names just the CPU core by itself; it does not capture bundling the surrounding subsystems (memory controllers, I/O, etc.) alongside it.

Hence, the correct term is System on a Chip (SoC).