If I have a market for smartphones let's say and demand for this good increases then this would create a shortage ceteris paribus and as a response the price would rise, right? But who actually raises this price in the real world? Is it the producer or the consumer (because I heard prices on ebay are determined by bidding)? An answer would be much appreciated
A rightward shift in the demand curve indicates only an increased willingness to pay by consumers as a whole. The actual price rise usually occurs when producers notice the good or service is selling faster than expected; the producer then increases the price as a method of rationing the remaining supply until rate of sales at the ask price aligns with future production capabilities at that new price. Therefore, it is typically the producer who allocates the supply to the consumers most willing to pay that price by increasing the price.
However, and less often, where consumers have knowledge or information that supplies are limited or are expected to become so, and they worry they may not be able to complete a purchase at the current market price, they may spontaneously increase their bid so that they can attract a guarantee of sale.