There's no fixed number as to how much they would like to see you do. I would say do enough where it becomes meaningful and becomes something unique and strong on your application. If you volunteered 150 hours, that's significant. However, if you volunteered 150 hours vs. 1000 hours...you have to weigh how significant that is, aside from you being extremely loyal to your organization. Instead, focus on what you learned and gained from your experience and be able to explain that in your essays and interviews. Of course, 10 hours is probably not enough, so use your own judgement.
In my experience, barely any pre-pharm students do research. There is probably less emphasis on volunteer than pre-med also, but it is definitely a plus. You can get into pharmacy school without experience, but it will be a lot harder. Adcoms want to know why you want to pursue the field and want someone to show they've actively thought about it; same as medical.