If you noticed chromosomes lined up near the middle of the cell, the cell would most likely be in

Metaphase

Cell division begins with Interphase, which signals the start of the cell division process. Here, the DNA in the cell duplicates to form chromosomes. 

The next phase is the Prophase where the chromosomes begin condensing and becoming more compacted and tightly wound. The mitotic spindle also starts forming at the edges of the cell. This would later on drive cell division by elongating the cell.

After prophase comes the Metaphase, where the pairs of chromosomes are pulled towards the opposite ends of the cell, causing them to be temporarily lined up at the center of the cell.

The pulling force pulls the chromosomes further towards the edge of the elongated cells in the next stage called the Anaphase. Here the cell also starts dividing.

Finally, the last phase, called the Telophase, marks the end of the cell division where the cells are eventually split into two in a process called cytokinesis.