In the polymeric title compound, [Co3(btc)2(phen)2(H2O)2]n [btc is the benzene-1,2,4-tricarboxylate trianion (C9H3O6) and phen is 1,10-phenanthroline (C12H8N2)], there are two different Co centres, Co1 and Co2. The Co1 centre has a deformed trigonal–bipyramidal geometry, while the Co2 centre lies on an inversion centre and has distorted octahedral geometry. Moreover, the 1,2-dicarboxylate groups of one btc ligand bridge the two adjacent Co2 centres, and each Co2 centre is coordinated by four carboxylate O atoms from four different btc ligands, forming a novel kind of intersecting double-chain structure, with a Co…Co separation of 7.755 Å, along the a axis. On the other hand, the two Co1 centres are bridged by two btc ligands and chelated by phen molecules, respectively, producing a binuclear unit with a Co…Co separation of 8.406 Å, and these binuclear units are linked by btc bridges and Co2 centres to extend hybrid chains of Co1 and Co2 along the  direction. Furthermore, each btc ligand acts as a pentadentate bridge, linking the Co2 double-chain structures and the hybrid chains of Co1 and Co2 to yield a two-dimensional network, and this leads to the formation of very different kinds of voids.