is there an option to answer a call on an iPhone6 on loudspeaker with one touch?

Not quite sure I understand, if a call comes in, then you get the answer/decline buttons show on the screen, you just tap whichever is appropriate, OneTouch doesn’t apply. Or you just click the button on a headset, if you’re wearing one.
Or tell Siri to answer, but I never use Siri, so I don’t know the protocol for answering calls.

Under settings, general, accesibilty. Incoming calls. Speaker

Thanks wysiwyg, I see what Tj was getting at now, having a blonde moment… 😳