I believe the use of the altar is compulsory for a Communion Service in a church.
According to the liturgical book “Holy Communion and the Worship of the Eucharist Outside of Mass”:
“19. When communion is given in a church or oratory, a corporal is to be placed on the altar, which is already covered with a cloth, and there are to be two lighted candles as a sign of reverence and festiveness. [Footnote 9: See GIRM no. 269] A communion plate is to be used.
When communion is given in other places, a suitable table is to be prepared and covered with a cloth; candles are also to be provided.”
In the 1988 Directory for Sunday Celebrations in the Absence of a Priest it explains how deacons use the presidential chair, but not lay people. Then it has in n. 40 “Since the altar is the table of sacrifice and of the paschal banquet, its only use in this celebration is for the rite of communion, when the consecrated bread is placed on it before communion is given.” What I think this means, following the liturgical book, is that the consecrated hosts should be put on the altar after the general intercessions. They stay there during the Our Father, Sign of Peace, “This is the Lamb of God …”. Then there will be communion.
Unfortunately (it seems to me) there is something different in “Pastoral Handbook for the Dioceses of Australia”, (published by National Liturigical Commission, 2004, ISBN 187552214X, page 30): “Since, ideally, the altar is not used in a Sunday celebration in the absence of a priest, the minister does not stand behind the altar. The leader of prayer remains at the place of leading the community’s prayer.” This is repeated in Appendix 3, page 40: “After the sign of peace and the Lord’s prayer (which may conclude with its doxology), the minister(s) of communion go to the tabernacle, open it, genuflect and bring the Blessed Sacrament to the front of the sanctuary for the distribution of communion. The altar is not used, and the ciborium lid is left at the tabernacle.”
The Australian book seems fairly official. Foreward by Most Reverend Kevin Manning, chairman, National Liturgical Commission, dated November 2003. Part of it is the 1988 Directory. Another part is Directives from the Australian Catholic Bishops Conference, saying sensible things like “7. The provisions of the Directory for Sunday Celebrations in the Absence of a Priest (1988) are to be observed in governing and directing liturgical ministry and worship …”. But another part of the book contradicts this, with “The altar is not used”.