If the person offering you the job knows you'd rather be doing a PhD, they will not be surprised if you keep looking for one (they may even recommend you to a colleague). Almost certainly you will be on a months notice in your technicians post. Which means that you can start a PhD a month after being offered it. This will be plenty of time, nobody will expect you to start straight away. Taking the technicians post should enhance your chances of being offered a PhD, as you will have experience of working in a lab environment.