Back away (http://www.usingenglish.com/reference/phrasal-verbs/back+away.html)
Retreat or go backwards
Back down (http://www.usingenglish.com/reference/phrasal-verbs/back+down.html)
Retract or withdraw your position or proposal in an argument
Back off (http://www.usingenglish.com/reference/phrasal-verbs/back+off.html)
Retreat
Back out (http://www.usingenglish.com/reference/phrasal-verbs/back+out.html)
Fail to keep an arrangement or promise
Back out of (http://www.usingenglish.com/reference/phrasal-verbs/back+out+of.html)
Fail to keep an agreement, arrangement
Back up (http://www.usingenglish.com/reference/phrasal-verbs/back+up.html)
Make a copy of computer data
Support

Be after (http://www.usingenglish.com/reference/phrasal-verbs/be+after.html)
Try to find or get
Be along (http://www.usingenglish.com/reference/phrasal-verbs/be+along.html)
Arrive
Be away (http://www.usingenglish.com/reference/phrasal-verbs/be+away.html)
- Be elsewhere; on holiday, etc.
Be cut out for (http://www.usingenglish.com/reference/phrasal-verbs/be+cut+out+for.html)
- Be suitable, have the necessary qualities
Be cut up (http://www.usingenglish.com/reference/phrasal-verbs/be+cut+up.html)
- Be upset
Be down (http://www.usingenglish.com/reference/phrasal-verbs/be+down.html)
- Be depressed
- Be reduced or less
Be down with (http://www.usingenglish.com/reference/phrasal-verbs/be+down+with.html)
- Be ill
Be fed up (http://www.usingenglish.com/reference/phrasal-verbs/be+fed+up.html)
- Be bored, upset or sick of something
Be in (http://www.usingenglish.com/reference/phrasal-verbs/be+in.html)
- Be at home or at work
- Be submitted, arrive
Be in on (http://www.usingenglish.com/reference/phrasal-verbs/be+in+on.html)
- Be involved in
Be not on (http://www.usingenglish.com/reference/phrasal-verbs/be+not+on.html)
- Be unacceptable
Be off (http://www.usingenglish.com/reference/phrasal-verbs/be+off.html)
- Be bad (of food)
- Depart, leave
Be on (http://www.usingenglish.com/reference/phrasal-verbs/be+on.html)
- Be functioning (of machines)
- Take place
- Take medication or drugs, especially when they affect the person badly
Be on about (http://www.usingenglish.com/reference/phrasal-verbs/be+on+about.html)
- Mean, try to say
Be onto (http://www.usingenglish.com/reference/phrasal-verbs/be+onto.html)
- Pursue, be aware of someone's true nature
Be out (http://www.usingenglish.com/reference/phrasal-verbs/be+out.html)
- Be absent from a place
Be out of (http://www.usingenglish.com/reference/phrasal-verbs/be+out+of.html)
- Have no more left
Be out to (http://www.usingenglish.com/reference/phrasal-verbs/be+out+to.html)
- Attempt
Be snowed under (http://www.usingenglish.com/reference/phrasal-verbs/be+snowed+under.html)
- Have too much work
Be taken aback (http://www.usingenglish.com/reference/phrasal-verbs/be+taken+aback.html)
- Be shocked or surprised
Be taken with (http://www.usingenglish.com/reference/phrasal-verbs/be+taken+with.html)
- Like something
Be up (http://www.usingenglish.com/reference/phrasal-verbs/be+up.html)
- Be out of bed
- Have increased or risen
- When the time for something finishes or expires
Be up to (http://www.usingenglish.com/reference/phrasal-verbs/be+up+to.html)
- Be good enough
- Doing something naughty or wrong