Im reading a book at the moment which says separation anxiety starts at around 6 months and they can't tell that you're coming back, so they get upset (not all bubs of course). Im not sure when they start to realise you will be back, but there is an age, so I would say it's a phase. They suggest just cuddling and making sure baby feels safe with you. The old advice was to get them used to it.... but nowadays they say the more secure they feel with you, the more independent they will become. (Once toddlers different story, but for bubs this is what my book says). I think it's called Heart to Heart parenting, got it from the ABC shop, fantastic! xo